System.Net.Mail - Trying to send a mail with attachment to gmail, works but for small attachments only

I use this class to send mails trough a gmail account:

public class GmailAccount
    {
        public string Username;
        public string Password;
        public string DisplayName;

        public string Address
        {
            get
            {
                return Username + "@gmail.com";
            }
        }

        private SmtpClient client;

        public GmailAccount(string username, string password, string displayName = null)
        {
            Username = username;
            Password = password;
            DisplayName = displ开发者_如何学JAVAayName;

            client = new SmtpClient
            {
                Host = "smtp.gmail.com",
                Port = 587,
                EnableSsl = true,
                DeliveryMethod = SmtpDeliveryMethod.Network,
                UseDefaultCredentials = false,
                Credentials = new NetworkCredential(Address, password)
            };
        }

        public void SendMessage(string targetAddress, string subject, string body, params string[] files)
        {
            MailMessage message = new MailMessage(new MailAddress(Address, DisplayName), new MailAddress(targetAddress))
            {
                Subject = subject,
                Body = body
            };

            foreach (string file in files)
            {
                Attachment attachment = new Attachment(file);
                message.Attachments.Add(attachment);
            }

            client.Send(message);
        }
    }

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Here is an example of how I use it:

GmailAccount acc = new GmailAccount("zippoxer", "******", "Moshe");
acc.SendMessage("zippoxer@gmail.com", "Hello Self!", "like in the title...", "C:\\822d14ah857.r");

The last parameter in the SendMessage method is the location of an attachment I want to add.

I tried sending a mail with an attachment of 400KB, worked great (even 900KB works). But then I tried uploading an attachment of 4MB, didn't work. Tried 22MB -> didn't work too.

There should be a limit of 25MB per message in Gmail. My message's subject and body are almost empty so don't consider them as part of the message's size. Why do I have that low limit?

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According to this post, it is a bug in .Net 4.0. The limit specified in the post is 3,050,417 bytes. You can try the work-around code included in the post. Hope this helps.

http://connect.microsoft.com/VisualStudio/feedback/details/544562/cannot-send-e-mails-with-large-attachments-system-net-mail-smtpclient-system-net-mail-mailmessage

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It's still possible to send. Just change the attachment encoding to something other than Base64. I tried testing this and found that there is a IndexOutOfBoundsException in the Base64 encoding code. I was able to successfully send an 11MB file to myself using TransferEncoding.SevenBit.

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Check and see if the SmtpClient object is going out of scope or otherwise being disposed before the send is complete and has sent the QUIT to the server.

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Okay, this is a bug in .net 4. Microsoft says it will be fixed in the next service pack.